JP3232532B2 - Austenitic stainless steel excellent in antibacterial property and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to kitchen appliances, electric appliances,
The present invention relates to an austenitic stainless steel suitable for applications requiring antibacterial properties in a wide range of fields such as building materials, mechanical devices, and chemical devices, and a method for producing the same.

[0002]

2. Description of the Related Art Corrosion resistance in general environments is required for various equipment used in kitchen equipment and hospitals, and handrail pipes for transportation such as buses and trains.
Stainless steel represented by 304 is mainly used. However, recently, in-hospital infections caused by Staphylococcus aureus and the like have become a problem, and there is a demand for improved hygiene even in an environment used by an unspecified number of people such as buses and trains. Along with this, the materials used for various machines and instruments are not limited to the properties of general structural materials, and are maintenance-free with functions such as antibacterial properties that do not require regular disinfection and other infection prevention. Material is desired. JP-A-5-228202 discloses a material having antibacterial properties.
As disclosed in Japanese Unexamined Patent Application Publication No. Hei 6-10191, an organic film and an antibacterial coat by plating are generally used.

[0003]

However, the antibacterial coat has a drawback that the antibacterial property is reduced as the film disappears.
The organic matter having lost the antibacterial property may become a nutrient source and may propagate bacteria and various bacteria. In the case of applying a composite plating mixed with an antibacterial agent component, the adhesion of the plating layer is not sufficient, and there is a drawback that the workability is reduced. In addition, the appearance may be deteriorated due to the dissolution, abrasion, chipping or the like of the film, and the antibacterial effect may be reduced. Incidentally, it is known that metal elements such as Ag and Cu exert an effective antibacterial action. However, Ag is extremely expensive and has poor corrosion resistance, and therefore is not used in applications exposed to an environment where corrosion is expected. On the other hand, since Cu is a relatively inexpensive element and is also effective as an antibacterial component, it has been studied to add it to a material such as stainless steel to impart antibacterial properties.

The present inventors have also studied various improvements in antibacterial properties by adding Cu, and found that the antibacterial properties can be improved by increasing the Cu concentration on the surface of stainless steel. No. 8-225895. The present invention has been devised in order to further enhance the action of Cu previously proposed. By precipitating a predetermined amount of a second phase mainly composed of Cu (hereinafter, referred to as a Cu-rich phase), an excellent antibacterial property is obtained. It is intended to impart the property to austenitic stainless steel.

[0005]

SUMMARY OF THE INVENTION The austenitic stainless steel of the present invention has a C content of 0.1%.
1% by weight or less, Si: 2% by weight or less, Mn: 5% by weight or less, Cr: 10 to 30% by weight, Ni: 5 to 15% by weight, and Cu: 1.0 to 5.0% by weight, with the balance being the balance Has a substantially Fe composition, and is characterized in that the Cu-rich phase precipitated by the aging treatment is dispersed in the matrix at a rate of 0.2% by volume or more. This austenitic stainless steel further contains Nb and / or Ti: 0.02 to 1% by weight, M
o: 3% by weight or less, Al: 1% by weight or less, Zr: 1% by weight or less, V: 1% by weight or less, B: 0.05% by weight or less, and rare earth element (REM): 0.05% by weight or less One or more kinds can be included. The Cu-rich phase is dispersed and precipitated in the matrix by subjecting an austenitic stainless steel having a predetermined composition to an aging treatment at least once in a temperature range of 500 to 900 ° C. from after hot rolling to a final product. I do.

[0006]

The stainless steel has excellent corrosion resistance because its surface is covered with a hydroxide mainly composed of Cr called a passive film. The present inventors have added Cu exhibiting effective antibacterial properties to austenitic stainless steel, measured the amount of Cu contained in the passive film, and investigated the antibacterial properties by dropping a liquid containing Staphylococcus aureus. did. As a result, it was found that stainless steel containing Cu to a certain degree or more had antibacterial properties. However, merely dissolving a few percent or less of Cu in steel may not always have sufficient antibacterial properties and durability. Therefore, as a result of further study, even if the Cu content is the same, if a part of Cu is finely and uniformly precipitated as a Cu-rich phase such as ε-Cu, the elution of Cu in the use environment And the antibacterial property was improved. Moreover, even if the surface is worn during processing or use, the internal Cu-rich phase appears on the new surface, so that the antibacterial durability is excellent.

As means for precipitating a Cu-rich phase,
It is conceivable that isothermal heating such as aging is performed in a temperature range where the Cu-rich phase is likely to precipitate, and that the passage time in the precipitation temperature range is made as long as possible by slow cooling. Then, as a result of examining various conditions, after final annealing, it is 500 to 900 ° C.
It has been found that when aging treatment is carried out within the range, precipitation is promoted, and good antibacterial properties can be obtained even when the Cu addition amount is low. In addition, when elements such as Ti, Nb, and Mo, which easily form carbonitrides and precipitates, are added, Cu-rich phases are easily dispersed in the matrix as precipitation sites for these precipitates and the like, and antibacterial properties and productivity are improved. Is done. When a part of Cu is precipitated as a Cu-rich phase, the Cu concentration on the surface increases and the antibacterial property is improved.

Hereinafter, alloying elements contained in the austenitic stainless steel of the present invention and their contents will be described. C: 0.1% by weight or less C is an alloy element effective for generating a Cr carbide effective as a precipitation site of a Cu-rich phase and uniformly dispersing a fine Cu-rich phase. However, if added in excess, the manufacturability and corrosion resistance deteriorate, so the upper limit of the C content is 0.1%.
It was restricted to wt%. Si: 2% by weight or less Si is an alloy element effective for improving corrosion resistance, and also exhibits an action of improving antibacterial properties. However, excessive Si addition exceeding 2% by weight deteriorates the productivity.

Mn: not more than 5% by weight It has an effect of improving manufacturability and fixing harmful S in steel as MnS. In addition, MnS acts as a nucleus for generating a Cu-rich phase, and is therefore an effective alloy element for precipitating a fine Cu-rich phase. However, a large content of Mn exceeding 5% by weight deteriorates corrosion resistance. Cr: 10 to 30% by weight Cr is an alloy element necessary for maintaining the corrosion resistance of austenitic stainless steel, and is required to contain 10% by weight or more of Cr in order to secure the required corrosion resistance. But 3
If a large amount of Cr exceeding 0% by weight is contained, manufacturability and workability deteriorate.

Ni: 5 to 15% by weight An important alloying element for stabilizing the austenite phase. However, since the addition of a large amount consumes expensive Ni and raises the cost of steel materials, the upper limit of the Ni content is restricted to 15% by weight. Cu: 1.0 to 5.0% by weight and Cu rich phase:
0.2% by volume or more It is the most important alloying element in the stainless steel of the present invention. In order to maintain good antibacterial properties, it is necessary that 0.2% by volume or more of a Cu-rich phase is precipitated. In order to precipitate a Cu-rich phase of 0.2% by volume or more in the austenitic stainless steel of the present system, a Cu content of 1.0% by weight or more is required. However, when an excessive amount of Cu exceeding 5.0% by weight is contained, manufacturability, workability, and corrosion resistance deteriorate. The Cu-rich phase is not particularly limited in the size of the precipitate, but in order to uniformly exhibit antibacterial properties over the entire product surface, and to maintain good antibacterial properties even when subjected to polishing or the like. Preferably, the precipitate phase is appropriately dispersed and distributed on the surface and inside.

Nb: 0.02 to 1% by weight The Cu-rich phase tends to precipitate around Nb precipitates. Therefore, in order to uniformly precipitate the Cu-rich phase, a structure in which Nb carbides, nitrides, and carbonitrides are finely precipitated is preferable. However, if Nb is excessively added, the manufacturability and workability deteriorate. From such a thing,
When adding Nb, it is preferable to adjust the content in the range of 0.02 to 1% by weight. Ti: 0.02 to 1% by weight As in the case of Nb, it forms a carbonitride and exhibits an effect of uniformly depositing a Cu-rich phase around it. However, excessive addition of Ti deteriorates manufacturability and workability, and easily causes flaws on the product surface. Therefore, when adding Ti, it is preferable to set the content in the range of 0.02 to 1% by weight.

Mo: 3% by weight or less Mo is an alloying element that is added as necessary, exhibits an effect of improving corrosion resistance, and precipitates as an intermetallic compound such as Fe ₂ Mo to form a fine Cu-rich phase nucleus site. And facilitates precipitation. In addition, Mo and a compound containing Mo exhibit an action of improving antibacterial properties by themselves. However, excessive Mo addition exceeding 3% by weight deteriorates the manufacturability and processability. Al: 1% by weight or less Like Mo, improves corrosion resistance and forms precipitates,
It is an effective alloy element for the precipitation of a fine Cu-rich phase. However, excessive addition of Al deteriorates manufacturability and workability. Therefore, when Al is added, the upper limit is restricted to 1% by weight. Zr: 1% by weight or less Zr is an alloy component added as needed, forms a carbonitride, and facilitates precipitation of a fine Cu-rich phase. However, if it is added excessively, the manufacturability and workability deteriorate. Therefore, when Zr is added, the upper limit is restricted to 1% by weight.

V: 1 wt% or less Carbon nitrides are formed in the same manner as Zr, thereby facilitating the precipitation of a fine Cu-rich phase. However, if it is added excessively, the manufacturability and workability deteriorate. Therefore, when V is added,
The upper limit is restricted to 1% by weight. B: 0.05% by weight An alloy component added as necessary, which improves hot workability and is dispersed as a precipitate in a matrix. However, if added excessively, hot workability deteriorates. Therefore, when B is added, the upper limit is restricted to 0.05% by weight. Rare earth element (REM): 0.05% by weight or less It is an alloy component added as needed. Hot workability is improved as in B by adding an appropriate amount. Further, it becomes a precipitate effective for the precipitation of the Cu-rich phase and is dispersed in the matrix. However, if added excessively, hot workability deteriorates. Therefore, when REM is added, the upper limit is regulated to 0.05% by weight.

Heat treatment temperature: 500-900 ° C. In order to precipitate a Cu-rich phase, 500-900 ° C.
Is effective. The lower the aging temperature, the lower the amount of solute Cu in the matrix and the greater the amount of Cu-rich phase deposited. However, if the aging treatment temperature is too low, the diffusion rate becomes slow, and the amount of precipitation decreases on the contrary. As a result of examining the temperature range effective for antibacterial properties by performing various aging treatments by changing temperature conditions, it is possible to perform aging treatment for 1 hour or more at a temperature range of 500 to 900 ° C in an industrially effective temperature range. I found it to be. This aging treatment is effective regardless of the stage after the hot rolling to the final product.

[0015]

EXAMPLES 30 kg of austenitic stainless steel having the composition shown in Table 1 was melted in a vacuum melting furnace, and subjected to annealing or aging treatment after forging and hot rolling to obtain a hot-rolled annealed plate. Then, cold rolling and annealing are repeatedly performed, and finally the sheet thickness is reduced to 0.1 mm.
A 7 mm cold-rolled annealed plate was obtained. For the sheet that was not subjected to the aging treatment after the hot rolling, the aging treatment was performed after the final annealing.
The aging time after hot rolling and after final annealing is 100
Set to time. The obtained test material was observed with a transmission electron microscope, and the amount of precipitated Cu-rich phase was quantified. In addition, each test piece was subjected to the following antibacterial test. Staphyloc
Ocusaureus IFO12732 (Staphylococcus aureus) was cultured with shaking in a normal broth medium at 35 ° C. for 16 to 24 hours to prepare a culture solution. The culture was diluted 20,000-fold with sterile phosphate buffer to prepare a bacterial solution. 5cm
× 5cm test piece # 400 polished surface 1ml of bacterial solution
Was added dropwise and stored at 25 ° C. for 24 hours. After storage, the test piece was washed off with 9 ml of SCDLP medium (manufactured by Nippon Pharmaceutical Co., Ltd.), and the number of viable cells was counted on the obtained liquid by a pour plate method (cultured at 35 ° C. for 2 days) using a standard agar medium. . Further, as a reference, a bacterial solution was directly dropped on a petri dish, and the number of viable bacteria was similarly counted.

A sample in which no viable cells were detected was indicated by ◎, and a sample in which 95% or more of the cells were killed as compared with the reference viable cell count was indicated by ○, 60
Those killed in a range of less than 95% were evaluated as Δ, and those killed in less than 60% were evaluated as x. Table 1 shows the evaluation results of the antibacterial properties together with the amount of precipitated Cu. As seen in Table 1, 1.0% by weight or more of Cu was added and C
Test Nos. 1 to 4 in which the amount of precipitation of the u-rich phase is 0.2% by volume or more
No. 13 shows good antibacterial properties. In contrast, in Test No. 18 in which the aging treatment was not performed even when the Cu content was 1.0% by weight or more, the amount of the Cu-rich phase deposited was less than 0.2% by volume, and the antibacterial properties were poor. . Also,
As can be seen in Test Nos. 17, 15, and 16, the amount of the Cu-rich phase precipitated was less than 500 ° C. or less than 90 ° C.
When the temperature exceeded 0 ° C., it was less than 0.2% by volume. From this, it is understood that the improvement of the antibacterial property requires the Cu content of 1.0% by weight or more and the Cu-rich phase precipitation of 0.2% by volume or more. In addition, it can be seen that aging treatment at 500 to 900 ° C. is effective in obtaining a Cu-rich phase precipitation amount of 0.2% by volume or more.

[0017]

[Table 1]

[0018]

As described above, the austenitic stainless steel of the present invention has a Cu content of 1.0% by weight.
As described above, since the Cu-rich phase precipitation amount is 0.2% by volume or more, excellent antibacterial properties are exhibited even with a solid material. Since this antibacterial property is derived from the material, it lasts for a long time. Therefore, this stainless steel is used in a wide range of fields where antibacterial properties are required, such as kitchen equipment, various equipment used in hospitals, etc., and equipment that comes into contact with the human body in transportation such as trains and buses. The living environment is improved.

Continuation of front page (72) Inventor Sadayuki Nakamura 4976 Nomura Minamicho, Shinnanyo-shi, Yamaguchi Prefecture Nissin Steel Works, Ltd. Technical Research Laboratory (56) References JP-A-6-17197 (JP, A) JP-A-6-134503 (JP, A) JP-A-7-188740 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46

Claims (2)

(57) [Claims] 1. C: 0.1% by weight or less, Si: 2% by weight
Mn: 5% by weight or less, Cr: 10 to 30% by weight,
Ni: 5 to 15% by weight and Cu: 1.0 to 5.0% by weight
Austenite excellent in antibacterial properties, in which the balance is substantially Fe, and the Cu-rich phase precipitated by aging is dispersed in the matrix at a rate of 0.2% by volume or more.
Series stainless steel. Subjecting 2. A method according to claim 1 austenitic stainless steel having the composition described in the temperature range of 500 to 900 ° C. until a final product after hot rolling to an aging treatment at least once, 0.2 Cu-rich second phase at a rate of at least volume%
A method for producing an austenitic stainless steel having excellent antibacterial properties, characterized by being precipitated .